Semiconductor device formation is commonly conducted in substrate processing systems or platforms containing multiple chambers, which may also be referred to as cluster tools. In some instances, the purpose of a multi-chamber processing platform or cluster tool is to perform two or more processes on a substrate sequentially in a controlled environment. In other instances, however, a multiple chamber processing platform may only perform a single processing step on substrates. The additional chambers can be employed to maximize the rate at which substrates are processed. In the latter case, the process performed on substrates is typically a batch process, wherein a relatively large number of substrates, e.g. 25 or 50, are processed in a given chamber simultaneously. Batch processing is especially beneficial for processes that are too time-consuming to be performed on individual substrates in an economically viable manner, such as for atomic layer deposition (ALD) processes and some chemical vapor deposition (CVD) processes.
The concept of spatial ALD is based on a clear separation of different gas phase reactive chemicals. Mixing of the chemicals is prevented to avoid gas phase reactions. The general design of a spatial ALD chamber may include a small gap between susceptor (or wafer surface) and gas injector. This gap can be in the range of about 0.5 mm to about 2.5 mm. Vacuum pumping channels are positioned around each chemical showerhead. Inert gas purge channels are between the chemical showerheads to minimize gas phase mixing. While current injector designs are able to prevent gas phase mixing the reactive species, the injectors do not provide enough control over where and when precursor exposure happens. There is an ongoing need in the art for apparatus and methods for controlling the flow of gases into a processing chamber.
In existing designs, as the precursor (or gas) begins to flow into the injector, the gas starts by charging the center of the injector and working outwards along the face of an injector plenum. When the injector is fully charged at steady state, precursor distribution is relatively uniform. Until the injector is fully charged, a large gas distribution non-uniformity exists. There is a need in the art for apparatus and methods to rapidly change gases in an injector while minimizing the amount of time to reach steady state gas distribution.